This invention relates to compression release mechanisms for internal combustion engines.
It is often desirable to relieve the pressure in an engine combustion chamber during starting. By relieving this pressure, it is much easier for the piston to reciprocate in the engine when the operator manually pulls the starter rope. A compression release mechanism thus lessens the pull force required to start the engine, and minimizes operator fatigue during starting.
Several types of compression release mechanisms are known for internal combustion engines. A typical compression release mechanism is disclosed in U.S. Pat. No. 3,381,676 issued May 7, 1968 to Campen. The Campen compression release mechanism includes a centrifugally-responsive flyweight, a torsion spring attached to the flyweight, and a central pin which engages a valve tappet at engine starting speeds. At higher engine speeds, the flyweight moves radially outward so that the pin disengages the valve tappet when the engine is running.
The Campen compression release mechanism has several disadvantages. First, it requires major modifications to the cam shaft to include a central pin member therein. Also, the shaft about which the flyweight rotates must be fastened to the flyweight, resulting in additional complexity and expense.
Other compression release mechanisms overcome some of the problems in the '676 Campen patent. For example, U.S. Pat. No. 3,496,922 issued Feb. 24, 1970 to Campen discloses a centrifugally-responsive flyweight having a torsion spring attached thereto, and a compression release shaft interconnected with the flyweight. The compression release shaft has a D-shaped end that engages a valve tappet. However, the compression release shaft must still be connected to the flyweight using a pin or other fastener, thereby increasing the complexity and difficulty in manufacture.
U.S. Pat. No. 3,362,390 issued Jan. 9, 1968 to Esty is another centrifugally-responsive compression release mechanism using a compression release shaft having a D-shaped end. However, the Esty patent requires fasteners to retain the torsion spring, again increasing the complexity and expense of the device.